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Chimney Help! - Forno Bravo Forum: The Wood-Fired Oven Community


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Chimney Help!

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  • Chimney Help!

    So I am about to finish up my dome and so I am trying to think ahead a little bit. So, I have decided that I am going to build a brick chimney (mostly due to cost but also because I think that I am going to have left over brick) but I have the following questions:

    1. If I decide to cast a base for the first coarse to sit on (I think I will need to because of my arch), is there a special mix that I will need to do the concrete out of?

    2. Is there a minimum height that I should build my chimney that will improve my draw?

    3. Is there any recommendations on chimney cap manufactures/designs for this type of chimney?

    4. Are there any special considerations that I need to make where my roofing materials butt up against the chimney since this system is not a double walled system?

    5. Any other tips or recommendations?


  • #2
    Re: Chimney Help!

    A typical masonry chimney has a flue tile liner, which is supported by the firebox, surrounded by a half inch air space between it and the masonry exterior, which is separately supported from the foundation. Because of this airspace, the masonry doesn't get very hot at all, hence the direct contact with the asphalt shingles. There is no contact between the two layers, even in quite tall chimneys, until the chimney cap, which if it is cast in place is surrounded by flashing so the two are separate, for purposes of thermal expansion.

    Building code calls for a two inch clearance to combustibles where a chimney goes through a wooden framed roof.

    There's no reason other than expense why this inner liner couldn't be made out of firebrick, but it would make for a larger (and heavier) structure.
    My geodesic oven project: part 1, part 2


    • #3
      Re: Chimney Help!

      My Chimney is 3' (3 12" clay chimney tile liners surrounded by brick). It draws great. I think the flue transition is as important as the height.
      My oven build: http://www.fornobravo.com/forum/f8/m...and-13300.html


      • #4
        Re: Chimney Help!

        If you want to cast a base for your chimney to sit on, you should probably use a castable refractory, which is a fireproof concrete and is available from refractory suppliers. It should be shaped like a funnel to extract the smoke efficiently and the chimney height can be as short or as tall as you like, but remember that the taller the stack the greater the draw.
        Kindled with zeal and fired with passion.


        • #5
          Re: Chimney Help!

          We visited the island of Paros in October and saw lots of different chimney top designs. There were hardly any two the same, all were different. Here are a couple.
          Attached Files
          Kindled with zeal and fired with passion.


          • #6
            Re: Chimney Help!

            Thanks for the help!


            • #7
              Re: Chimney Help!

              I think I understand this a little better but I still have a couple other questions now that I have thought about this a little more.

              1. If I do a clay flue liner with an enclosure, does anyone see any issues with not starting my brick chimney until the clay liner goes though the framed enclosure (other than making the enclosure strong enough to support the brick which should not be an issue). My thought is that this will greatly reduce the amount of brick that I need to lay for the chimney which will in turn reduce the weight on my front archs.

              2. If the clay liner is exposed until it reaches the roof line (all while keeping a safe distance for from potentially flammable materials), should I insulate the flue with a ceramic blanket?

              3. For those of you who have enclosures.....Does anyone install soffit vents or roof vents to give the warm air a place to escape as it heats up? Or is this a non-issue?

              Thanks again....I can't wait to fire this baby up!!!


              • #8
                Re: Chimney Help!

                Unless you can find a way to start the brick lower than the roofline (shouldn't be hard to do... a couple of short pieces of steel stud), you are going to have a hotspot at the roof deck. Also, it will be a lot easier to flash the chimney if the brick starts below the decking, you will be able to cut a reglet joint in the mortar. mklingles, i wish that i had made my flue transition a little larger... i have a 36" oven with 24" of SS double wall flue mounted to a SS base... i am going to have to add at least another foot of pipe..


                • #9
                  Re: Chimney Help!

                  Code says that (enclosed) clay flue liner has to have a masonry wrap, which is good sense because thy are prone to cracking. Your entry way should be able to handle the weight, or it should be redesigned to do so.

                  I considered soffit vents but in the end did not put any in. My oven was totally cured by the time it was enclosed though.


                  • #10
                    Re: Chimney Help!

                    Thanks again guys....you have answered all of my questions.